1. Field of the Invention
The present invention relates to a magnetic head, a head gimbal assembly, a hard disk drive, and a method of manufacturing a magnetic head.
2. Related Background Art
In recent years, the areal density of hard disk drives has been increasing remarkably. Most recently, in particular, the areal density of hard disk drives has reached 160 to 200 Gigabytes/platter and is about to increase further. Consequently, thin-film magnetic heads have been required to improve their performances,
Widely employed as a magnetic head is a combination thin-film magnetic head having a structure in which a recording head with an inductive electromagnetic transducer for writing and a reproducing head with a magnetoresistive device (MR device) for reading are laminated on each other.
A typical recording head comprises upper and lower magnetic pole layers having magnetic pole parts partly opposing each other by way of a gap layer on the side opposing a recording medium, a link part for magnetically linking the upper and lower magnetic pole layers, and a thin-film coil helically wound about at least one of the magnetic pole layers while in a state insulated from the upper and lower magnetic pole layers. The side of the recording head (magnetic head) opposing the recording medium is referred to as a medium-opposing surface or air bearing surface.
For raising the recording density among recording head performances, the track density in the recording medium is required to increase. To this aim, it is necessary to realize a recording head having a narrow track structure in which the track width, i.e., the width of the two magnetic pole parts opposing each other across the gap layer on the medium-opposing surface, is reduced to a size on the order of several microns to submicron. For realizing such a recording head, semiconductor processing techniques have been in use.
As the track width is made smaller, it becomes harder for magnetic fluxes with a high density to occur between the two magnetic pole parts opposing each other across the gap layer. Therefore, it has been desired that a magnetic flux material having a higher saturated magnetic flux density be employed as a material for the magnetic pole parts.
As the frequency of recording signals rises in order to increase the recording density, the recording head is required to improve the magnetic flux changing rate, i.e., shorten the flux rise time, and reduce deterioration in recording characteristics such as overwrite characteristic and non-linear transition shift in a high-frequency band. Shortening the magnetic path length has been known effective in improving recording characteristics in the high-frequency band. The magnetic path length is mainly determined by the length (referred to as “yoke length” in this specification) of the part between the link part and the medium-opposing surface in the lower or upper magnetic pole layer. Therefore, shortening the yoke length is effective in reducing the magnetic path length. For shortening the yoke length, it will be effective if the pitch of turns of the thin-film coil, the part of turns arranged between the link part and the medium-opposing surface in particular, is made smaller.
Meanwhile, for example, U.S. Pat. Nos. 6,043,959 and 6,191,916B1 disclose magnetic heads in which a flat spiral thin-film coil is disposed about a link part. In thus configured magnetic head, many magnetic fluxes occur in the vicinity of the link part. These magnetic fluxes are guided by the lower and upper magnetic pole layers to the magnetic pole part of the head, so as to be used as magnetic fluxes for recording.
However, the magnetic fluxes generated by the thin-film coil cannot efficiently be used as magnetic fluxes for recording in the magnetic head having the above-mentioned structure. Namely, it has been known that only a few percent of magnetic fluxes generated by the thin-film coil can be used as magnetic fluxes for recording in a magnetic head having such a structure. Therefore, the number of turns has been raised in thus configured magnetic head in order to increase the magnetic fluxes used for recording.
As a technique for reducing the pitch of turns of the thin-film coil, the above-mentioned U.S. Pat. No. 6,191,916B1 discloses a technique in which turns of the second coil are disposed between those of the first coil.
On the other hand, U.S. Pat. No. 5,995,342, Japanese Patent Application Laid-Open No. 2000-311311, and U.S. Pat. No. 6,459,543B1 disclose magnetic heads having a thin-film coil helically wound about at least one of the lower and upper magnetic pole layers. In such a magnetic head, the thin-film coil is partly disposed between the link part and the medium-opposing surface. In thus configured magnetic head, magnetic fluxes generated by the thin-film coil are efficiently used as magnetic fluxes for recording. Therefore, this magnetic head can make the number of turns of the thin-film coil smaller than that in the magnetic head having a flat spiral thin-film coil, whereby the yoke length is significantly shortened.
As mentioned above, it is desirable that the yoke length be made shorter in order to improve recording characteristics of a magnetic head in the high-frequency band. For this purpose, reducing the pitch of turns of the thin-film coil disposed between the link part and the medium-opposing surface is effective. On the other hand, increasing the number of turns of the thin-film coil is desirable for improving the recording characteristics of the magnetic head.
In any of the magnetic heads having a flat spiral thin-film coil and the magnetic heads having a helical thin-film coil, the width of the part of the thin-film coil disposed between the link part and medium-opposing surface must be made smaller in order to increase the number of turns of the thin-film coil while shortening the yoke length. This increases the ohmic value of the thin-film coil, so that a greater amount of heat is generated, whereby the magnetic pole part may project toward and collide with the recording medium. Hence, it is not so desirable to simply reduce the width of the coil in order to shorten the yoke length.
Thin-film coils are usually formed by frame plating. The frame used in the frame plating has a wall part disposed between adjacent turns in the thin-film coil. For keeping the shape of the wall part, the width thereof must have a certain extent. Therefore, when forming a thin-film coil by frame plating, it has been difficult to reduce the gap between adjacent turns of the thin-film coil.
Using the technique disclosed in Patent Document 2, the gap between adjacent turns in a flat spiral thin-film coil can be reduced. In the magnetic head disclosed in the above-mentioned U.S. Pat. No. 6,191,916B1, however, magnetic fluxes are generated by a flat spiral thin-film coil, whereby the magnetic fluxes generated by the thin-film coil cannot efficiently be used as magnetic fluxes for recording as mentioned above.